KR101260592B1 - Method for producing metallic carbon nanotube, carbon nanotube dispersion liquid, carbon nanotube-containing film, and transparent conductive film - Google Patents

Abstract

It is to provide a method for producing metallic carbon nanotubes in which a high concentration of dispersion is obtained. Metallic carbon nano comprising a fullerene addition step of adding fullerene to a carbon nanotube-containing solution in which the metallic carbon nanotubes and the semiconducting carbon nanotubes are mixed, and a extraction step of taking out the carbon nanotubes dispersed by the added fullerene. Method of making the tube.

Description

METHOD FOR PRODUCING METALLIC CARBON NANOTUBE, CARBON NANOTUBE DISPERSION LIQUID, CARBON NANOTUBE-CONTAINING FILM, AND TRANSPARENT CONDUCTIVE FILM}

The present invention relates in particular to metallic carbon nanotubes.

In recent years, the demand of a transparent conductive film is rapidly increasing by the market expansion of the thin display device represented by a liquid crystal display. A transparent conductive film is used for an electrode, for example. Or it is used for a resistive touch panel. Or it is used for an electromagnetic shield film. In addition, it is used for various uses. This kind of transparent conductive film is generally composed of a metal oxide such as InSn oxide (ITO). Transparent conductive films such as ITO are formed by a method such as sputtering. Therefore, high temperature is required for film formation by these methods. For this reason, the use of the resin substrate lacking heat resistance is large. Furthermore, the vacuum atmosphere is needed for film-forming. For this reason, as a board | substrate becomes large, a huge film forming apparatus is needed. Therefore, the cost of film formation is expensive. In is difficult to obtain since In is a rare metal. Therefore, also in this point, cost is expensive.

In this regard, alternative techniques have been proposed to replace ITO. In particular, a technique of forming a carbon nanotube film by a coating method has been proposed. Moreover, the transparent conductive film using a carbon nanotube has high evaluation.

By the way, among the carbon nanotubes, single-walled carbon nanotubes are said to have the highest conductivity. However, single layer carbon nanotubes do not disperse well in the solvent. Therefore, it is not easy to construct a single-walled carbon nanotube conductive film by coating. Thus, the use of dispersants has been proposed. For example, use of sodium dodecyl sulfate is proposed (nonpatent literature 1). Moreover, use of sodium dodecyl benzene sulfonate is proposed (nonpatent literature 1). Moreover, use of octyl phenol polyethylene glycol ether is proposed (nonpatent literature 1). Moreover, the use of sodium cholate is proposed (nonpatent literature 2). Moreover, use of polyvinylpyrrolidone is proposed (nonpatent literature 3).

Japanese Patent Publication No. 2006-013788 Japanese Unexamined Patent Publication No. 2008-055375

 M.F.Islam et al NANO LETTERS 2003, Vol. 3, 269  T. Hertel et al. NANO LETTERS 2005, Vol. 2, 511  Michael J. O'Connell et al. Chemical Physics Letters 342 (2001) 265

However, even when sodium dodecylbenzenesulfonate (dispersant) is used in large quantities, only a low concentration of single-walled carbon nanotube dispersions can be obtained. For example, in the nonpatent literature 1, although 20 mass% of sodium dodecylbenzene sulfonate is used with respect to a solvent, only the low concentration single layer carbon nanotube dispersion liquid was obtained.

When polyvinylpyrrolidone (dispersant) is used (nonpatent literature 3), a high concentration single layer carbon nanotube dispersion liquid is obtained. However, it is not possible to remove the dispersant (polyvinylpyrrolidone). For this reason, even if the film | membrane of a single | mono layer carbon nanotube is formed, the electroconductivity of this single layer carbon nanotube membrane is low. Therefore, it is difficult to use this as a transparent conductive film.

As described above, in the conventional technique, even when a large amount of the dispersant is used, only a low concentration of single-walled carbon nanotube dispersion can be obtained. For this reason, practical coating methods, such as a bar coat, could not be employ | adopted.

Single-layer carbon nanotube dispersions using organic solvents such as tetrahydrofuran and dimethylformamide have been proposed. However, tetrahydrofuran is highly toxic. Moreover, dimethylformamide has a boiling point too high. Therefore, the use of these solvents is not preferred. That is, practical use is difficult.

In this respect, a single-walled carbon nanotube dispersion dispersed in a solvent such as water or an alcohol (eg, alcohol such as methanol or 2-propanol) is desired.

However, when water (water only) was used as a solvent until now, wettability was bad and dispersibility was bad.

However, it is pointed out that metallic carbon nanotubes and semiconducting carbon nanotubes exist in the carbon nanotubes. Here, metallic carbon nanotubes mean single layer carbon nanotubes which do not have a band gap in the axial direction. Specifically, when the chiral vector (Ch) of a single-walled carbon nanotube is represented by the following formula [Ch = (n, m), where n and m are all integers], n-m is a multiple of 3. Can be. The semiconducting carbon nanotubes refer to single-walled carbon nanotubes with a band gap in the axial direction. Specifically, when the chiral vector (Ch) of a single-walled carbon nanotube is represented by the following formula [Ch = (n, m), where n and m are all integers], n-m is not a multiple of 3. Can be mentioned. And it is imagined that semiconducting carbon nanotubes are inferior in conductivity compared with metallic carbon nanotubes. Therefore, when carbon nanotubes are used for the transparent conductive film, it is preferable to preferentially use metallic carbon nanotubes. That is, when carbon nanotubes are used as components of the conductive film, it is preferable to make the ratio of the metallic carbon nanotubes relatively high even when the semiconductor carbon nanotubes and the metallic carbon nanotubes are contained together.

However, the method (separation method) of taking out metallic carbon nanotube preferentially from the carbon nanotube which a metallic carbon nanotube and a semiconducting carbon nanotube mixed is not proposed much. For example, the method of using the difference of the adsorption force of octylamine is proposed (patent document 1). Moreover, the method using the electrophoresis method is proposed (patent document 2). However, these methods have a problem that the carbon nanotube content of the resulting dispersion is low. In addition, there is a problem that it can be applied only to short carbon nanotubes.

Accordingly, the problem to be solved by the present invention is to solve the above problems.

In particular, it is to provide a method for producing metallic carbon nanotubes capable of obtaining a high concentration of dispersion.

Moreover, it is providing the technique which can manufacture the transparent conductive film which has high electroconductivity and transparency using a metallic carbon nanotube by simple application | coating technique.

We pushed forward examination to solve the problem mentioned above. As a result, the inventors found that when fullerene (in particular, fullerene having an OH group) is used, even when water is used as the solvent, the dispersibility of the carbon nanotubes is improved. In particular, it has been found that fullerene (in particular, fullerene having an OH group) preferentially acts on metallic carbon nanotubes rather than acting on semiconducting carbon nanotubes. That is, under the conditions in which the semiconducting carbon nanotubes and the metallic carbon nanotubes are mixed, when fullerene (particularly, fullerene having an OH group) is added, the fullerene is preferentially bonded to the metallic carbon nanotubes. As a result, it was found that the metallic carbon nanotubes were preferentially dispersed in the solution. Since the semiconducting carbon nanotubes were not dispersed in the solution, it was found that the semiconducting carbon nanotubes could be removed by solid-liquid separation means (for example, centrifugal separation or the like).

In addition, when a semiconducting carbon nanotube and a metallic carbon nanotube exist in a bundle state, it is difficult to carry out this bundle state only by adding a fullerene. Therefore, it is desirable to bundle the semiconducting carbon nanotubes with the metallic carbon nanotubes. In this case, it was also found that it can be realized by, for example, ultrasonic irradiation.

Moreover, when using the fullerene dispersion liquid of the carbon nanotube containing more metallic carbon nanotube, it turned out that the transparent conductive film which has high electroconductivity and transparency can be comprised by a simple application | coating means.

Based on these findings, the present invention has been achieved.

That is, the above problem,

A fullerene mixing step of mixing carbon nanotubes and fullerenes in which metallic carbon nanotubes and semiconducting carbon nanotubes are mixed;

It is solved by the manufacturing method of the metallic carbon nanotube characterized by including the extraction process which takes out the carbon nanotube dispersed in the solution by the said mixed fullerene.

For example, the fullerene addition process of adding fullerene to the carbon nanotube containing solution in which a metallic carbon nanotube and a semiconducting carbon nanotube are mixed,

It is solved by the manufacturing method of the metallic carbon nanotube characterized by including the extraction process which takes out the carbon nanotube dispersed by the added fullerene.

In addition, the carbon nanotubes in which the metallic carbon nanotubes and the semiconducting carbon nanotubes are bundled may be bundled to form a bundle,

A fullerene mixing step of mixing carbon nanotubes and fullerenes in which metallic carbon nanotubes and semiconducting carbon nanotubes are mixed;

It is solved by the manufacturing method of the metallic carbon nanotube characterized by including the extraction process which takes out the carbon nanotube dispersed in the solution by the said mixed fullerene.

For example, by performing a bundle state of the carbon nanotubes in which the metallic carbon nanotubes and the semiconducting carbon nanotubes are bundled,

A fullerene mixing step of mixing the carbon nanotubes and fullerene in which the metallic carbon nanotubes and the semiconducting carbon nanotubes are mixed before or after the above-described step or during the above-described step;

It is solved by the manufacturing method of the metallic carbon nanotube characterized by including the extraction process which takes out the carbon nanotube dispersed by the said mixed fullerene.

Moreover, as said invention, the carbon nanotube in which a metallic carbon nanotube and a semiconducting carbon nanotube exist in bundle form is solved by the manufacturing method of metallic carbon nanotube characterized by the above-mentioned.

Moreover, as said invention, the said process is solved by the manufacturing method of the metallic carbon nanotube characterized by the ultrasonic irradiation process which irradiates an ultrasonic wave to the carbon nanotube which exists in the said bundle state.

Moreover, as said invention, the said ultrasonic irradiation process is solved by the manufacturing method of the metallic carbon nanotube characterized by the ultrasonic output 300-800 W and ultrasonic irradiation time 10 minutes or more.

Moreover, as said invention, the said fullerene is solved by the manufacturing method of the metallic carbon nanotube characterized by the fullerene which has an OH group.

Moreover, as said invention, the solvent of the solution containing the said carbon nanotube is any selected from the group of water, alcohol, and the mixed solution of water and alcohol, By the manufacturing method of the metallic carbon nanotube characterized by the above-mentioned. Resolved.

In addition, the above problem,

Carbon nanotubes having at least 50% metallic carbon nanotubes,

Fullerene having an OH group,

It is solved by a carbon nanotube dispersion liquid containing a solvent.

In particular, a carbon nanotube having a metallic carbon nanotube of 50% or more,

Fullerene having an OH group,

Containing solvents,

The solvent is solved by a carbon nanotube dispersion, wherein the solvent is any one selected from the group of water, alcohol, and a mixed solution of water and alcohol.

In addition, the above problem,

Carbon nanotubes having at least 50% metallic carbon nanotubes,

It is solved by a carbon nanotube-containing film characterized by containing a fullerene having an OH group.

In addition, the above problem,

Carbon nanotubes having at least 50% metallic carbon nanotubes,

It is solved by the transparent conductive film characterized by containing the fullerene which has OH group.

In the present invention, even a carbon nanotube, a so-called metallic carbon nanotube is mainly used. That is, since content of semiconducting carbon nanotubes was reduced, the electroconductivity of the obtained transparent conductive film improved.

Selective separation of metallic carbon nanotubes depends on the adoption of fullerenes. In addition, the use of fullerene also plays a role in improving the dispersibility of metallic carbon nanotubes. Therefore, it is very preferable.

The metallic carbon nanotube dispersion liquid containing fullerene has very good dispersibility of the carbon nanotubes. In particular, even if the concentration of carbon nanotubes is high, dispersibility is good. Furthermore, even if water (or alcohols) is used as the solvent, the dispersibility of the carbon nanotubes is good. In particular, the amount of fullerene (dispersant) is at least very good in dispersibility of the carbon nanotubes.

As a result, the transparent conductive film which has high electroconductivity and transparency can be comprised by simple application | coating means.

And it can use advantageously as a transparent electrode, a touch panel member, and an electromagnetic shielding material, for example.

The present invention is a method of producing (drawing out: separating) metallic carbon nanotubes. The present invention has a fullerene addition (mixing) process. For example, it has a fullerene addition (mixing) process of adding (mixing) fullerene to the carbon nanotube-containing solution in which the metallic carbon nanotubes and the semiconducting carbon nanotubes are mixed. Moreover, it has the extraction process which takes out the metallic carbon nanotube dispersed by the added (mixed) fullerene.

In general, carbon nanotubes (for example, single-walled carbon nanotubes) exist in a bundle of metallic carbon nanotubes and semiconducting carbon nanotubes. Even if fullerene is added to the carbon nanotube-containing solution which exists in such a bundle state, only metallic carbon nanotube cannot be fractionated only by it. Therefore, when the metallic carbon nanotubes and the semiconducting carbon nanotubes are present in a bundled state, a process is required by performing the bundled state.

The said process is an ultrasonic irradiation process which irradiates an ultrasonic wave, for example. For dispersion, ultrasonic irradiation is commonly used. However, the ultrasonic irradiation for carrying out the bundled state needs to be stronger than the ultrasonic irradiation for dispersion. For example, the ultrasonic irradiation for carrying out a bundle state is preferably ultrasonic irradiation with an output of 10-1000W. More preferably, it is ultrasonic irradiation whose output is 100 W or more. More preferably, it is the ultrasonic irradiation whose output is 300-800W. The ultrasonic irradiation time is preferably 10 to 1000 minutes. More preferably, it is 20 to 60 minutes. In addition, in the case of a small output, irradiation time becomes relatively long. On the contrary, in the case of a large output, irradiation time may be short.

A bath type ultrasonic irradiator can be used for ultrasonic irradiation. Moreover, the cone type ultrasonic irradiation machine can also be used. Other ultrasonic devices may be used. It is preferable to use a cone-type ultrasonic irradiator from the viewpoint of obtaining a more powerful output.

If the metallic carbon nanotubes and the semiconducting carbon nanotubes are present independently (possibly apart) through the above process, the added fullerene preferentially acts (bonds) to the metallic carbon nanotubes. As a result, the metallic carbon nanotubes are preferentially dispersed. In contrast, semiconducting carbon nanotubes without fullerene action (bonding) have low dispersibility. Since the semiconducting carbon nanotubes have low dispersibility, the metallic carbon nanotubes can be easily separated and extracted by the solid-liquid separation method. After fullerene addition (mixing), it is preferable to perform ultrasonic irradiation for enhancing dispersibility. Addition (mixing) of said fullerene is after a process, for example, as it came to the bundle state of a metallic carbon nanotube and a semiconducting carbon nanotube. However, if the fullerene is affected by the operation, the operation is different. However, since the fullerine is not chemically modified by ultrasonic irradiation, the fullerene may be added (mixed) in advance during the operation.

The extraction step of taking out the metallic carbon nanotubes dispersed by fullerene is, for example, a step such as centrifugation or filtration. For example, it is preferable to employ a step of centrifuging the solution and recovering the supernatant after fullerene addition (mixing). As a result, the undispersed carbon nanotubes are removed, thereby obtaining a conductive film having higher transparency. If the centrifugal separation is too strong, the dispersed metallic carbon nanotubes are also removed. On the contrary, if too weak, undispersed semiconducting carbon nanotubes cannot be removed. Therefore, it is preferable to carry out on conditions of 10000G-100000G (it is 30000G or more and 50000G or less). The treatment time is preferably about 1 to 48 hours. In particular, about 5 to 24 hours are more preferable. By going through this step, a more uniformly dispersed metallic carbon nanotube dispersion liquid can be obtained. In place of the centrifugal separation step, or before (and / or after) the centrifugal step, for example, a filtration step may be employed. That is, a method of taking out (separation: removal) by filtration can also be used. Various filtration methods are used for filtration. For example, suction filtration, pressure filtration, or cross flow filtration can be used.

The present invention is a carbon nanotube dispersion. This carbon nanotube dispersion liquid contains a carbon nanotube (mainly metallic carbon nanotube), fullerene, and a solvent. In particular, a carbon nanotube having a proportion of the metallic carbon nanotubes of 50% or more, fullerene having a OH group, and a solvent are contained. In addition, the ratio of semiconducting carbon nanotube is 50% or less. Preferably, the semiconducting carbon nanotubes are substantially free of content. Of course, the case where the semiconducting carbon nanotubes are not contained (substantially zero within the range of detection error) is more preferable. That is, the semiconducting carbon nanotubes are removed as much as possible, in that the carbon nanotubes obtained through the production (takeout: separation) method of the metallic carbon nanotubes of the present invention are used. For example, it does not substantially contain semiconducting carbon nanotubes. In such a metallic carbon nanotube dispersion, the ratio of the carbon nanotubes (metallic carbon nanotubes) and fullerene is 10 to 1000 parts by mass of fullerenes in particular with respect to 100 parts by mass of carbon nanotubes (metallic carbon nanotubes). The fullerene concentration is in particular 1 to 100000 ppm (preferably 10 ppm or more, more preferably 100 ppm or more. 10000 ppm or less, and even 5000 ppm or less). Fullerene is preferably fullerene having a polar group. Especially, fullerene which has an OH group is preferable. In addition, since fullerene exhibits a dispersing action, it is not necessary to basically use another dispersant, but it is not to be used. In addition, you may add the agent which suppresses electroconductivity fall with the temperature of a carbon nanotube as needed. For example, a polymer having a sulfonic acid group may be added.

The carbon nanotubes in which the metallic carbon nanotubes and the semiconducting carbon nanotubes used in the present invention are bundled are, for example, single-walled carbon nanotubes. Preferably, it is a single-walled carbon nanotube obtained by the arc discharge method. And, More preferably, it is the wet-oxidation single layer carbon nanotube. The content of the wet oxidation treatment is reflux for 24 hours or longer with, for example, 50% or more nitric acid or a mixed acid of nitric acid and sulfuric acid.

0.03 의 조건을 만족한다.Preferred single-walled carbon nanotubes satisfy the following conditions. In the Raman intensity distribution characteristic detected by laser irradiation of wavelength 532 nm, it has a 1st absorption in the intensity | strength of a Raman scattered light in the range whose Raman shift is 1340-40 Kaiser. In addition, it has a second absorption in the intensity of the Raman scattered light in a range in which the Raman shift is 1590 ± 20 Kaiser. 0 <(strength of the first absorption) / (strength of the second absorption)

The condition of 0.03 is satisfied.

Single-layer carbon nanotubes exist in a bundle state in a solution. And it is preferable that the number of bundles of length exceeding 1.5 micrometers satisfy | fills more conditions than the number of bundles of 1.5 micrometers or less in length. Alternatively, the bundle is present in a bundle state, and the bundle length is not a single length, but has a predetermined distribution, and the predetermined distribution is a condition in which the mode in the frequency distribution for every 0.5 μm of the bundle exceeds 1.5 μm. It is desirable to satisfy. Especially, it is preferable to satisfy all the said conditions.

Various things are used for the carbon nanotube dispersion liquid of this invention as a solvent. However, as a solvent used, water, alcohol (especially aliphatic alcohol with 7 or less carbon atoms), or mixed liquids such as this are preferable. In particular, the solvent which contains water at least is preferable. And it is preferable that a solvent is a thing whose pH exceeded 7 (that is, showing alkalinity). When the absorbance is measured without dilution, the carbon nanotube dispersion liquid has a local maximum of absorbance derived from single-walled carbon nanotubes in the range of 400 nm to 800 nm, and the maximum is preferably 0.1 or more and 5 or less.

The film | membrane obtained by apply | coating (for example, 10 nm-1000 nm thick application | coating) the said metallic carbon nanotube dispersion liquid on a base material (especially a transparent base material) contains a metallic carbon nanotube and fullerene basically. . However, since the carbon nanotube obtained by the extraction (separation) method of the said metallic carbon nanotube is used, the semiconducting carbon nanotube is removed as much as possible. For example, it does not substantially contain semiconducting carbon nanotubes. The dispersion is, for example, for a transparent conductive film. Therefore, the obtained coating film is a transparent conductive film, for example.

It will be described in more detail below.

The fullerene used in the present invention may be any fullerene. For example, C60, C70, C76, C78, C82, C84, C90, C96 etc. are mentioned. Of course, the mixture of multiple types of fullerenes, such as this, may be sufficient. In addition, C60 is particularly preferable from the dispersion performance. Moreover, C60 is easy to obtain. Moreover, not only C60 but also a mixture of C60 and other fullerenes (for example, C70) may be sufficient. Fullerene may be a metal atom appropriately contained therein. It is preferable that fullerene has a functional group (polar group: For example, hydroxyl group (OH group), carboxyl group, epoxy group, ester group, amide group, sulfonyl group, ether group, etc.). Moreover, fullerene which has a phenyl-C61-propyl acid alkyl ester and a phenyl-C61-butyl acid alkyl ester may be sufficient. Moreover, hydrogenated fullerene may be sufficient. However, as mentioned above, fullerene which has an OH group (hydroxyl group) is especially preferable. This is because the dispersing ability to the metallic carbon nanotubes is high. In addition, when the number of OH groups is small, the degree of dispersibility improvement of the carbon nanotubes is not large. If the number of OH groups is large, the synthesis of fullerene is difficult. Therefore, the number of OH groups is preferably 5 to 30 (per molecule of fullerene). In particular, 8-15 pieces are preferable.

Here, the reason why fullerene raises the dispersibility of metallic carbon nanotube is considered as follows. The benzene ring and the metallic carbon nanotube contained in fullerene are physically adsorbed by π-π interaction. And fullerene acts as a functional group of a metallic carbon nanotube externally. For this reason, it is thought that the dispersibility of metallic carbon nanotubes improved. In addition, in the above, what was described "appearance" is because the bond of a fullerene and metallic carbon nanotube is not a chemical bond but a physical bond (adsorption). In addition, the π-π interaction is larger than that of the conventionally proposed surfactant. In other words, fullerene is strongly adsorbed on the metallic carbon nanotubes, thereby increasing the dispersibility of the metallic carbon nanotubes. In addition, the semiconducting carbon nanotubes and fullerene are not physically bound. For this reason, it is considered that semiconducting carbon nanotubes do not have high dispersibility.

By the way, it is understood that it is preferable to use fullerene which has a polar group as long as it is a solvent which has a polar group. This is because fullerene having a polar group is more easily dissolved in a polar solvent (for example, water or alcohol) than a nonpolar solvent. Therefore, in view of the dispersibility of the metallic carbon nanotubes, it is preferable to use fullerene having a polar group as described above.

When using a metallic carbon nanotube dispersion liquid as a coating material, it is preferable to use water (or / and alcohol) as a solvent from a viewpoint of reducing an environmental load or improving a working environment. When such a solvent is used, the fullerene has a functional group (polar group; for example, hydroxyl group (OH group), carboxyl group, epoxy group, ester group, amide group, sulfonyl group, ether group, etc.) It is preferred that it is fullerene. In particular, fullerene which has an OH group (hydroxyl group) is especially preferable because water and alcohol have an OH group.

The concentration of fullerene is preferably 1 ppm to 100,000 ppm. In particular, 10 ppm-10000 ppm are preferable. Especially, 100 ppm-5000 ppm are preferable. This is because when the fullerene concentration is too high, the viscosity becomes too high, which makes coating difficult. On the contrary, when it is too low, the dispersibility improvement degree of metallic carbon nanotube will not be large.

Carbon nanotubes used for the transparent conductive film of the present invention are particularly metallic carbon nanotubes. This is because the conductivity is higher than that of the semiconducting carbon nanotubes or other known carbon materials. This metallic carbon nanotube is separated from the single-walled carbon nanotubes, for example. In the single-walled carbon nanotubes, for example, metallic carbon nanotubes and semiconducting carbon nanotubes are present in a bundled state. Therefore, when this bundle state is opened, metallic carbon nanotube can be taken out selectively.

Single-walled carbon nanotubes form a bundle even in a solution. Here, a bundle means the state (shape) in which the single-walled carbon nanotubes overlap with each other by van der Waals forces of side walls. In addition, the single-walled carbon nanotubes produced by a conventionally known method are obtained in a bundle state. The length of this bundle has some distribution. However, it is preferable to have the following characteristics. That is, the single-walled carbon nanotubes have a certain distribution in the length of the bundle. For example, the number of bundles whose length exceeds 1.5 m is greater than the number of bundles whose length is 1.5 m or less. Preferably, the number of bundles having a length of 2.0 μm or more is greater than the number of bundles having a length of 1.5 μm or less. More preferably, the number of bundles having a length of 2.5 μm or more is larger than the number of bundles having a length of 1.5 μm or less. Or the mode in the frequency distribution (frequency distribution table or frequency distribution chart) for every 0.5 micrometer of bundle length exceeded 1.5 micrometers. Preferably, the mode in the frequency distribution of a bundle length exceeds 2.0 micrometers. More preferably, the mode in the frequency distribution of a bundle length exceeds 2.5 micrometers. And when a bundle has a distribution of the said characteristic, all were excellent in transparency and electroconductivity.

The following method is used to measure the bundle length. Single-walled carbon nanotubes are observed with a scanning microscope and the length thereof is measured. However, it is not limited to this method. There is no particular limit on the number of bundles to measure. However, in order to obtain accurate statistical values, it is preferable to measure 50 or more bundles. Furthermore, 100 or more measurements are more preferable. When measuring the length of the bundle, when there are many impurities, the measurement becomes difficult. Therefore, it is preferable to measure after removing an impurity to a measurable degree. Moreover, in a state where a bundle is dense, length measurement is difficult. Therefore, it is preferable that it is disperse | distributed to the density which can measure each bundle one by one. There is no restriction | limiting in particular in the form of the frequency distribution chart (table) with respect to the length of a bundle. For example, any of symmetric distribution, asymmetric distribution, J-shaped distribution, U-shaped distribution, and sealing property distribution may be sufficient. However, it is preferable that it is symmetrical distribution. In addition, a mode means the value of the highest rank among all the ranks. In the classification of the water supply, the setting of the range is aggregated in units of 0.5 µm.

{a/(a+b+c)}

0.40, 0.20

{b/(b+c)}

0.30 을 만족하는 것이 보다 바람직하다. 습식 산화의 반응 조건에 대해서도 각별한 제한은 없다. 단, 유효한 산 처리를 실시하기 위해서는, 반응 온도가 85 ℃ 이상인 것이 바람직하다. 반응 시간은 24 시간 이상, 나아가서는 48 시간 이상인 것이 바람직하다. 본 발명에 사용되는 단층 카본 나노 튜브는, 어떤 수법으로 제조된 것이어도 된다. 예를 들어, 아크 방전법, 레이저 증발법, 화학 기상 증착법 등으로 얻을 수 있다. 단, 결정성이나 수율의 관점에서, 아크 방전법으로 얻어진 단층 카본 나노 튜브를 사용하는 것이 바람직하다. 사용되는 단층 카본 나노 튜브는, 순도가 높은 것이 바람직하다. 순도가 낮으면, 투광률이 저하되기 때문이다. 단층 카본 나노 튜브의 순도는 라만 스펙트럼 측정에 의해 확인할 수 있다. 구체적으로는, 카본 나노 튜브를 구성하는 주성분인 그래핀 시트 유래의 흡수 강도와 그 이외의 탄소 재료를 나타내는 성분 유래의 흡수 강도비에 의해 카본 나노 튜브의 순도를 확인할 수 있다. 예를 들어, 아크 방전에 의해 제작된 단층 카본 나노 튜브를 파장 532 ㎚ 의 레이저를 조사하여 측정한 경우, 라만 시프트가 1340 ± 40 카이저인 범위에 라만 산란광의 강도에 제 1 흡수를 가짐과 함께, 라만 시프트가 1590 ± 20 카이저인 범위에 라만 산란광의 강도에 제 2 흡수를 갖는다. 여기서, 제 1 흡수는 그래핀 시트 유래의 흡수이고, 제 2 흡수는 탄소 원자의 sp³ 궤도 유래의 흡수라고 일컬어지고 있다. 그리고 제 1 흡수 강도에 대해 제 2 흡수 강도가 작은 편이, 카본 나노 튜브의 순도는 높다. 본 발명에 있어서의 단층 카본 나노 튜브는 다음의 조건을 만족하는 것이 바람직하다. 즉, 파장 532 ㎚ 의 레이저를 조사하여 검출되는 라만 강도 분포 특성에 있어서, 라만 시프트가 1340 ± 40 카이저인 범위에 라만 산란광의 강도에 제 1 흡수를 가짐과 함께, 라만 시프트가 1590 ± 20 카이저인 범위에 라만 산란광의 강도에 제 2 흡수를 갖고, 상기 제 1 흡수의 강도를 ID, 상기 제 2 흡수의 강도를 IG 로 했을 경우, 식 (1) 을 만족한 것이 바람직하다. 식 (2) 를 만족한 것이 특히 바람직하다. 즉, ID/IG 의 값이 0.03 이하인 경우에는, 순도가 높고, 투명성·도전성이 모두 우수한 것이었다. The carbon nanotubes (for example, single layer carbon nanotubes) used for separating and extracting the metallic carbon nanotubes are preferably wet oxidized. This is because dispersibility with respect to a solvent improves. Wet oxidation is not particularly limited. However, it is preferable to use inorganic acid (for example, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, or mixed acid thereof) for wet oxidation. In particular, it is preferable to use nitric acid of 50% or more, or a mixed acid of nitric acid and sulfuric acid. In the case of using a mixed acid of nitric acid and sulfuric acid, when the volume ratio of the entire mixed acid aqueous solution of water, nitric acid and sulfuric acid is a (vol%), b (vol%), c (vol%), 0.20

{a / (a + b + c)}

0.40, 0.20

{b / (b + c)}

It is more preferable to satisfy 0.30. There is no restriction | limiting in particular also about the reaction conditions of wet oxidation. However, in order to perform effective acid treatment, it is preferable that reaction temperature is 85 degreeC or more. The reaction time is preferably 24 hours or more, more preferably 48 hours or more. The single-walled carbon nanotubes used in the present invention may be produced by any method. For example, it can obtain by the arc discharge method, the laser evaporation method, the chemical vapor deposition method, etc. However, from the viewpoint of crystallinity and yield, it is preferable to use single-walled carbon nanotubes obtained by the arc discharge method. It is preferable that the single layer carbon nanotube used is high in purity. It is because light transmittance will fall when purity is low. The purity of single layer carbon nanotubes can be confirmed by Raman spectroscopy. Specifically, the purity of the carbon nanotubes can be confirmed by the absorption strength ratio derived from the graphene sheet, which is the main component constituting the carbon nanotubes, and the absorption strength ratio derived from the components representing other carbon materials. For example, when the single-wall carbon nanotubes produced by arc discharge were measured by laser irradiation with a wavelength of 532 nm, the Raman shift had a first absorption in the intensity of the Raman scattered light in the range of 1340 ± 40 Kaiser, It has a second absorption in the intensity of the Raman scattered light in the range where the Raman shift is 1590 ± 20 Kaiser. Here, 1st absorption is absorption derived from a graphene sheet, and 2nd absorption is called absorption derived from the sp <^3> orbital of a carbon atom. The smaller the second absorption intensity relative to the first absorption intensity is, the higher the purity of the carbon nanotube is. It is preferable that the single-walled carbon nanotube in this invention satisfy | fills the following conditions. That is, in the Raman intensity distribution characteristic detected by irradiating a laser having a wavelength of 532 nm, Raman shift has a first absorption in the intensity of the Raman scattered light in a range in which the Raman shift is 1340 ± 40 Kaiser, and the Raman shift is 1590 ± 20 Kaiser. It is preferable to satisfy | fill Formula (1), when it has the 2nd absorption in the intensity | strength of Raman scattered light in the range, and set the intensity of the said 1st absorption as ID, and the intensity of the said 2nd absorption as IG. It is especially preferable to satisfy Formula (2). That is, when the value of ID / IG was 0.03 or less, it was high in purity and excellent in both transparency and conductivity.

0.03 Equation (1) 0 <ID / IG

0.03

0.02Equation (2) 0 <ID / IG

0.02

The solvent used by this invention should just be a solvent used with general coating materials. There is no particular limitation. However, the solvent whose boiling point is 200 degrees C or less (preferable minimum value is 25 degreeC, and also 30 degreeC) is preferable. The low boiling point solvent is preferable because drying after coating is easy. Specifically, water, alcohol compounds such as methanol, ethanol, normal propanol and isopropanol (particularly alcohols having 7 or less carbon atoms, especially aliphatic alcohols), or mixtures thereof and the like are preferable. When water is used, it is particularly preferable that the pH exhibits alkalinity of more than 7. This is because the solubility of hydroxyl-containing fullerene is high. In other words, a higher concentration of metallic carbon nanotube dispersion can be obtained. In addition, ketone compounds, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, can be used, for example. Moreover, ester compounds, such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and methoxy ethyl acetate, can be used. In addition, ether compounds such as diethyl ether, ethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, phenyl cellosolve and dioxane can be used. Moreover, aromatic compounds, such as toluene and xylene, can be used. In addition, aliphatic compounds such as pentane and hexane can be used. Moreover, halogen-type hydrocarbons, such as methylene chloride, chlorobenzene, and chloroform, can be used. Moreover, the mixture of the said compound can also be used.

The concentration of the metallic carbon nanotubes in the metallic carbon nanotube dispersion liquid can be quantified using a spectrophotometer. That is, by measuring the absorbance using a spectrophotometer, the concentration of the metallic carbon nanotubes can be quantified. That is, when a calibration curve is prepared and the proportional constant which shows the relationship between absorbance and mass ratio is calculated | required, concentration can be represented by mass ratio. In addition, the said proportional constant changes with metallic carbon nanotubes used.

The metallic carbon nanotube dispersion liquid obtained as mentioned above is apply | coated on a base material, and a transparent conductive film is obtained. As mentioned above, the metallic carbon nanotube dispersion liquid which becomes this invention has high dispersibility of metallic carbon nanotube. For example, it is disperse | distributed in favorable dispersibility to solvents, such as water and alcohol. Therefore, various coating methods, such as a spray coat, a bar coat, a roll coat, the inkjet method, and a screen coat, can be used.

The base material to which the metallic carbon nanotube dispersion liquid is applied is not particularly limited. For example, in a use where transparency is required, such as a transparent electrode used in a display or the like, a transparent substrate (a film or a sheet or a plate having a thickness greater than that of the film (sheet)) is preferable. For example, acrylic resin, polyester resin, polycarbonate resin, polystyrene resin, styrene-acrylic acid copolymer, vinyl chloride resin, polyolefin, ABS (acrylonitrile-butadiene-styrene copolymer), vinyl alcohol resin, cycloolefin Type resin, a cellulose resin, etc. can be used. In addition, an inorganic glass etc. can also be used. However, the base material made of organic resin which is excellent in flexible characteristics is preferable. On the surface of the base material (the surface on the side where the conductive layer is formed and / or the back side opposite to the side on which the conductive layer is formed), a hard coat layer, an antifouling layer, an antiglare layer, an antireflection layer, an adhesive layer, A colored layer or the like is formed (laminated). The thickness of a base material is determined according to the objective. However, in general, the thickness is about 10 to 10 mm.

After the said coating process, drying is performed in order to remove the solvent contained in a coating film. A heating furnace is used for drying. Moreover, you may use far infrared rays. Moreover, you may use meadow infrared rays. In addition, the apparatus which can be used for drying can be used normally.

The transparent conductive film excellent in electroconductivity and transparency is obtained as mentioned above. And the transparent conductive film excellent in electroconductivity and transparency can be used for the electrode substrate for touch panels. Moreover, it can use for the electrode substrate of an electronic paper. Moreover, it can use for the electrode substrate of a liquid crystal display. Moreover, it can use for the electrode substrate of a plasma display. In addition, it can use for various things.

Hereinafter, the present invention will be described with specific examples. It is obvious that the present invention is not limited to the following examples.

Example 1

Single layer carbon nanotubes were prepared by the arc discharge method. This prepared single-walled carbon nanotube was subjected to a wet oxidation treatment (for example, reaction at 85 ° C. for 2 days with 63% nitric acid). Thereafter, the single-walled carbon nanotubes were purified and recovered by filtration.

The bundle length of this purified monolayer carbon nanotube was investigated. As a result, it turned out that a mode exists in the range from 1.5 micrometers to 2.0 micrometers. And the ratio which occupies for the whole number of bundles of the single-walled carbon nanotube whose bundle length exceeded 1.5 micrometers was about 73%. The proportion of the bundles in the total number of bundles of single-walled carbon nanotubes having a length of 1.5 µm or less was about 27%. In addition, it was about 13% about 1.0 micrometer-1.5 micrometer, about 20% about 1.5 micrometer-2.0 micrometer, about 18% about 2.0 micrometer-2.5 micrometer, and about 13% about 2.5 micrometer-3.0 micrometer. That is, the number of bundles of single-walled carbon nanotubes having a bundle length of 1.5 µm or less was less than the number of bundles of single-walled carbon nanotubes having a bundle length exceeding 1.5 µm.

20 mg of the single-walled carbon nanotubes obtained as described above, 3 mg of hydroxyl group-containing fullerine (trade name manufactured by NANOSPECTRA D-100 Frontier Carbon, Inc .: fullerene is made of C60 fullerene), and 0.3 mg of sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) And 5 ml of water and 5 ml of isopropanol were mixed. The concentration of single layer carbon nanotubes was 2230 ppm.

Cone-type ultrasonic irradiator (output 650 W, frequency 40 Hz) was used for the mixed solution, and ultrasonic irradiation over 20 minutes was performed. As a result, the single-walled carbon nanotubes in the bundled state were released. That is, the single-walled carbon nanotubes were dissociated into metallic carbon nanotubes and semiconducting carbon nanotubes.

The hydroxyl group-containing fullerenes were bonded to the metallic carbon nanotubes, and the metallic carbon nanotubes were sufficiently dispersed in the water / alcohol solution. In contrast, the semiconducting carbon nanotubes were poorly dispersed in a water / alcohol solution.

Thereafter, a centrifuge (product name CR26H Hitachi Industrial Machinery Co., Ltd.) was used to perform centrifugal separation on the carbon nanotube dispersion. The conditions of centrifugation are 7 hours at 20000 rpm (48000 G). And the supernatant liquid after centrifugation was collect | recovered. This supernatant and the solution before sonication were irradiated with a spectrophotometer. As a result, it was confirmed that the supernatant liquid had more absorption of the metal component (650 nm) than the absorption (1010 nm) of the semiconductor component compared to before separation.

The supernatant after the centrifugal separation operation, i.e., the dispersion of the metallic carbon nanotubes (removing the semiconductor carbon nanotubes) was bar coat applied onto the polycarbonate substrate with a hard coat. Coating thickness (wet film thickness) is 50 micrometers. After application, drying was performed at 80 ° C. for 3 minutes. And the polycarbonate plate with a transparent conductive film was obtained. The conductivity of the conductive film of the polycarbonate plate with this transparent conductive film was investigated. As a result, electrical conductivity was 149 ohms / square, and there existed sufficient utility. Moreover, transparency was 74% and there was enough utility.

From the above results, according to the present invention, it was possible to obtain a high concentration dispersion which was impossible in the prior art (the concentration of the carbon nanotube disclosed in Patent Document 1 is 112 ppm), and the separation operation of the metal / semiconductor at a high concentration can be performed. there was.

[Example 2]

The commercially available metallic carbon nanotubes (IsoNanotubes-M: Metallic SWNTs manufactured by NanoIntegris) were subjected to centrifugal separation operation to carry out mixing and dispersion of the solids extracted, hydroxyl group-containing fullerene, sodium hydroxide, water, and isopropanol. . Thereafter, a centrifugal separation operation was performed. The supernatant was then bar coat applied onto a polycarbonate substrate with a hard coat. And drying was performed. Thereby, the polycarbonate plate with a transparent conductive film was obtained.

In addition, in this Example, a metallic carbon nanotube and a semiconducting carbon nanotube do not form a bundle. Therefore, the ultrasonic treatment for the bundle seaming performed in Example 1 was not performed.

The conductivity of the conductive film of the polycarbonate plate with the transparent conductive film was investigated. As a result, electrical conductivity was 1350 ohms / square, and there existed sufficient utility. Moreover, transparency was 78.68% and there was enough utility.

Comparative Example 1

The commercially available semiconducting carbon nanotubes (IsoNanotubes-S: Semiconducting SWNTs, manufactured by NanoIntegris) were subjected to centrifugal separation to mix and disperse solids extracted, hydroxyl group-containing fullerenes, sodium hydroxide, water, and isopropanol. It became. Thereafter, a centrifugal separation operation was performed. The supernatant was then bar coat applied onto a polycarbonate substrate with a hard coat. And drying was performed. Thereby, the polycarbonate plate with a transparent conductive film was obtained.

The conductivity of the conductive film of the polycarbonate plate with this conductive film was investigated. As a result, there was no conductivity which has utility. The reason why the conductive film of the present comparative example was not practically conductive was considered that no metallic carbon nanotubes were used, that is, only semiconductor carbon nanotubes were used. The semiconducting carbon nanotubes have poor dispersibility even when hydroxyl group-containing fullerene is used. As a result, it was considered that the amount of semiconducting carbon nanotubes contained in the supernatant after centrifugation was small.

This application claims the priority based on Japanese Patent Application No. 2008-274688 for which it applied on October 24, 2008, and takes in all the indication here.

Claims (12)

A fullerene mixing step of mixing a carbon nanotube and a fullerene in which a metallic carbon nanotube and a semiconducting carbon nanotube are mixed;
And a takeout step of taking out the carbon nanotubes dispersed in the solution by the mixed fullerene. The method of claim 1,
It is made by further providing a process by carrying out the bundle state of the carbon nanotube in which a metallic carbon nanotube and a semiconducting carbon nanotube exist in a bundle state,
A method for producing a metallic carbon nanotube, wherein the fullerene is mixed before the step, during the above step, or after the above step. The method of claim 2,
The carbon nanotubes in which the metallic carbon nanotubes and the semiconducting carbon nanotubes are present in bundles are single-walled carbon nanotubes. The method of claim 2,
The said process is an ultrasonic irradiation process which irradiates an ultrasonic wave to the carbon nanotube which exists in the said bundle state, The manufacturing method of metallic carbon nanotube characterized by the above-mentioned. The method of claim 4, wherein
The said ultrasonic irradiation process is an ultrasonic wave output of 300-800 W, and ultrasonic irradiation time is 10 minutes or more, The manufacturing method of the metallic carbon nanotube characterized by the above-mentioned. 6. The method according to any one of claims 1 to 5,
The fullerene is a method for producing a metallic carbon nanotube, characterized in that the fullerene having an OH group. 6. The method according to any one of claims 1 to 5,
The solvent of the solution containing the carbon nanotube is any one selected from the group of water, alcohol, and a mixed solution of water and alcohol. Carbon nanotubes having at least 50% metallic carbon nanotubes,
Fullerene having an OH group,
A carbon nanotube dispersion liquid containing a solvent. The method of claim 8,
The solvent is carbon nanotube dispersion liquid, characterized in that any one selected from the group of water, alcohol, and a mixed solution of water and alcohol. Carbon nanotubes having at least 50% metallic carbon nanotubes,
A carbon nanotube-containing film, characterized by containing a fullerene having an OH group. Carbon nanotubes having at least 50% metallic carbon nanotubes,
It contains fullerene which has OH group, The transparent conductive film characterized by the above-mentioned. The method according to claim 6,
The solvent of the solution containing the carbon nanotube is any one selected from the group of water, alcohol, and a mixed solution of water and alcohol.